My EU4 Strength Score next steps
Europa Universalis IV
You already have many Polish/Lithuanian/European monarchy achievements and military/early-powerplay ones, so doing Poland-specific tech (Poland can into space) plus becoming absolutist (One King to Rule!) and showcasing a cavalry power spike (Winged Hussars) form a tight, achievable trio that builds on your existing regional and military strengths.
Poland can into space
Winged Hussars